1. Field of the Invention
This invention relates to inventory selection systems, such as systems for selection or “picking” of inventory for order fulfillment.
2. Description of the Related Art
Retailers, wholesalers, rental services, and other product distributors (which may collectively be referred to as distributors) typically maintain an inventory of various items that may be ordered by clients or customers. Similarly, manufacturers may maintain an inventory of parts and/or materials for use in manufacturing processes. This inventory may be maintained and processed at materials handling facilities which may include, but are not limited to, one or more of: warehouses, distribution centers, cross-docking facilities, order fulfillment facilities, inventory rental facilities, packaging facilities, shipping facilities, factories, or other facilities or combinations of facilities for performing one or more functions of material (inventory) handling.
FIG. 1 illustrates a broad view of the operation of a conventional materials handling facility. Multiple customers 10 may submit orders 20 to the distributor, where each order 20 specifies one or more items from inventory 30 to be shipped to the customer that submitted the order. To fulfill the customer orders 20, the one or more items specified in each order may be retrieved or picked from inventory 30 (which may also be referred to as stock storage) in the materials handling facility, as indicated at 40. Picked items may be delivered or conveyed, if necessary, to one or more stations in the materials handling facility for sorting 50 into their respective orders, packing 60, and finally shipping 70 to the customers 10. Note that a picked, packed and shipped order does not necessarily include all of the items ordered by the customer; a shipped order may include only a subset of the ordered items available to ship at one time from one inventory-storing location. Also note that a materials handling facility typically also includes a receiving 80 operation for receiving new shipments 90 of stock from various vendors and placing the received stock into stock storage. The receiving 80 operation may also receive and process returned purchased or rented items 92 or orders from customers. At least some of these items are typically returned to inventory 30. Note that some items received in the receiving 80 operation may be delivered or “cross-docked” to other locations in the materials handling facility than inventory 30, for example to packing 60 or shipping 70. Further, note that the various operations of a materials handling facility may be located in one building or facility, or alternatively may be spread or subdivided across two or more buildings or facilities.
FIG. 2 illustrates an exemplary physical layout of a conventional materials handling facility, specifically an order fulfillment facility, or center. At any time, one or more agents 42 of the distributor may each be picking items from inventory 30 to fulfill portions or all of one or more orders. This may result in a stream and/or batches of picked items for multiple incomplete or complete orders, which may then be delivered to various stations (pick destinations 50), for example sorting or packing stations, in the materials handling facility for processing prior to shipping 70. A stream may be a continuous or nearly continuous flow of picked items arriving at a station, while groups of items arriving periodically or aperiodically at a station may be referred to as batches. Note that portions of an order may be received from the pickers 42, or from other stations, at a station at different times, so processing at a station may have to wait for one or more items for some orders to be delivered to the station from picking and/or from another station before completion of processing of the orders.
Agents, or pickers, 42 may receive instructions from a control system on a device such as an RF-connected wireless terminal or handheld scanner, to go to locations in inventory 30 to pick a list of items from those locations. A picker 42 typically scans a picked item to determine if the right item was picked. The picker 42 may then place the picked item in a receptacle for receiving picked items. The receptacle may be located on or integrated with a mobile cart of some type. The mobile cart may or may not be a powered vehicle. There may be more than one receptacle on a cart. Alternatively, the receptacle may be located on or integrated with a basket or chassis that is physically attached to or carried by the picker.
Conventionally, a picker 42 picks items from inventory 30 for only one pick destination 50 at a time. For example, a picker 42 may be instructed to pick items for one order at a time, or items for a batch of orders all going to one pick destination 50 (e.g., to a particular automated sorting station, manual sorting station, packing station, or other processing station), or a list of items from various orders all going to a particular destination, etc. Thus, a picker 42 picks items for one stream or process path for the items, delivers the picked items to their common pick destination 50, and leaves the processing and sorting of the picked items into their individual orders to the downstream station(s). The picker 42 then repeats the process for another list of items potentially for a different pick destination 50.
The stream or batches of incoming picked items are processed at a station, for example sorted into their respective orders at a sorting station. Once the processing of items for an order is completed at a station, the items may be delivered to another station for further processing, for example to a sorting station to be sorted into orders or to a packing station to be packaged for shipping 70.
Note that an order fulfillment center may also include one or more receiving 80 operations for receiving shipments 90 of stock from various vendors. The received stock may then be placed into stock storage. The receiving 80 operation may also receive and process returned, purchased, or rented items 92 from customers. At least some of these returned items 92 are typically returned to inventory 30. Also, Note that the various operations and stations of an order fulfillment center may be located in one building or facility, or alternatively may be spread or subdivided across two or more buildings or facilities.
Random Stow
In a materials handling facility, when a customer places an order, one or several inventory items specified in the order must be retrieved or picked from inventory and prepared for delivery to the customer. Conventionally, like items are stored together within inventory to facilitate inventory tracking and management. For example, items having a common Universal Product Code (UPC), Stock-Keeping Unit (SKU) code, or other designation (including proprietary designations) may be stored together within inventory. In an inventory environment that includes a large number of many different items, it may be highly inefficient for a single employee to locate and pick every item for a given order. For example, the different items specified by a given order may be stored at mutually remote locations within the inventory facility, which would require a single picking agent to traverse a long path through the facility.
In order to make better use of inventory stocking space, it may be desirable to stock different items together in a single storage location or stocking area. “Random-stow” is one technique of co-locating items in a materials handling facility in which any item may be stored in any slot in inventory 30 where physical space is sufficient. Given some inventory profiles, random-stow may be more efficient than more traditional inventory storage techniques, where like items are assigned to specific locations, and where a single slot, bin, container, receptacle, etc. typically contains items with at most one UPC, SKU code, or other designation.
Random-stow is a relatively broad term, in this context, meant to include any situation in which sets of heterogeneous products may be randomly or pseudo-randomly distributed in a single inventory location, and thus where conventionally one or more specific products may need to be removed from that location in such a way that the identity of the product being removed at a particular moment is known.
Random-stow methodology is not yet common in the logistics/storage industry because it requires computational resources that were too expensive 15+ years ago, and the industry is slow to adapt to new technology. Random-stow may become more common as logistics incorporates inexpensive information technology (IT) solutions, such as RFID technologies, and as the necessity to service “long tail” inventory profiles with many more SKUs than traditional storage techniques can handle grows. “Long-tail” refers to items in inventory that may have lower turnover rates, for example slow-moving items that are only occasionally ordered. Because of the low turnover rates, large quantities of long tail inventory are typically not kept in stock. For these types of items, it is inefficient to stow one product in one bin. Random-stow works well as a storage technique for these items.
One of the primary costs of random-stow is time spent at a bin for a picker to find the item requested. A conventional random-stow picking process requires an agent to walk to a receptacle (e.g., container, bin, tote, pallet, etc.) and then search it for the requested product(s) to be picked. Once the item is found in the bin, the agent can proceed to pick the item. Typically, this process is repeated for each pick from that bin. In some contexts, the walking portion of picking takes about half of the labor and the search portion takes the other half.
While increasing the efficient use of inventory space, co-location of different items, for example using a random-stow technique, may increase the difficulty, and thus the time, of identifying and picking a particular item. When picking items from inventory, the picking agent generally must examine any co-located items in order to determine the specific item to pick. This can be time-consuming in situations where numerous similar items are stored together. Additionally, several similarly titled or described items may be stored in a single inventory area, increasing the difficulty of identifying any particular item. For instance, if several CDs are entitled “Greatest Hits” and stored together, a picking agent may have to read the full title for each item in turn to identify the correct item. The extra time this requires may be significant when multiplied across the large number of orders fulfilled by a typical facility. Similarly, in a facility handling items for rent or sale, there may be a large number of similar-looking items, such as DVDs, stored together. A picking agent may have difficulty identifying particular DVDs from among multiple DVDs in a single inventory. Again, any extra time required to correctly identify a DVD becomes significant, since each DVD may be stored and picked many times, as it is rented and returned.